Two methyltransferase enzymes have been found to synthesize phosphatidyl choline from phosphatidylethanolamine in adrenal medulla and erythrocyte membranes. These enzymes have been found to be asymmetrically distributed in erythrocyte membranes and involved in the translocation of phospholipids from cytoplasmic to the outer surface of membranes. The enzymatic methylation of phosphatidylethanolamine to phosphatidyl N-monomethylethanolamine causes a profound change in membrane fluidity. Stimulation of the beta adrenergic receptor in reticulocyte ghosts causes an increase in methylation fluidity and translocation of phospholipids and coupling of beta adrenergic receptor with adenylate cyclase. More beta adrenergic receptors were found to be available to binding by its ligands when phospholipid methylation is increased by the addition of S adenosyl methionine reticulocyte ghosts.